This invention relates to semiconductor lasers and more particularly to multiple quantum well (MQW) lasers that have their operating or primary emission wavelength tuned selectively to a different emission wavelength. This invention is an improvement of and extension to Burnham et al, U.S. Pat. No. 4,589,115, issued May 13, 1986.
In U.S. Pat. No. 4,589,115, there is disclosed the method for tuning the wavelength of quantum well injection lasers, both single and multiple well type, using an external grating wherein the range of operating wavelength selection is extended, beyond the expectations of wavelength selection possible in bulk crystal heterostructure lasers, to include wavelength selection at the multiple carrier recombination transition energies possible in the conduction band subbands and valence band subbands existing in quantum well heterostructures. Quantum well heterostructure lasers have an unique advantage of being band filled to well above the bulk crystan band edge at moderate current densities indicative of broad band tuning through a wide range of quantum well subbands of the quantum well structure of such lasers U.S. Pat. No. 4,589,115 is incorporated herein by reference thereto.
MQW heterostructure lasers, however, are believed not to band fill as easily as a thin single quantum well (SQW) heterostructure laser because electrons tend to thermalize faster to the lowest subband states in MQW heterostructure lasers compared to SQW heterostructure lasers.
It is a principal object of this invention to extend the tuning range of MQW heterostructure lasers by effectively slowing down this thermalization process.